During drilling process, the swiveling drilling bit is installed on the drill rod, the sea level platform conducts the control to drill bit via the drill rod, and the drill rod drives the drill bit swiveling, in which way, the shaft is drilled out under seabed. During the mentioned period, the drilling fluid in the fluid tank that installed on the sea level platform reaches the drill bit via drill rod, then return to the fluid tank via the annular space formed between the drill rod and riser pipe. The drilling fluid maintains a certain level of hydrostatic pressure to balance the pressure of fluid from shaft and to cool down the drill bit. In addition, the drilling fluid mixes with the material generated during the formation of shaft to return and carry back the material to the sea surface for treatment.
During drilling process, when the pressure of fluid entering the shaft from the wellbore is larger than the pressure of drilling fluid, the fluid in strata enters the annular space with the drilling fluid, in this way, it would be generated that the drilling fluid is returned with greater pressure, further, there is a blowout in case of loss of control. Therefore, monitoring and measuring the returned drilling fluid in real time is necessary to determine whether the blowout will occur. In general, the flow rate of drilling fluid returned is measured to determine whether the fluid changes to monitor the occurrence of blowout, and to ensure the safety operation of drilling.
Drawing 1A shows the axial schematic drawing of a riser pipe and drawing 1B shows the horizontal schematic drawing of a riser pipe. As shown in drawing 1A and 1B, it is known that the flow rate vi of the drilling fluid 130 returned (as shown in drawing 3) that flowing in the riser pipe 11 in the direction in parallel with ultrasonic beam path could be calculated, then, under the condition that without any consideration of the horizontal flow rate component vR of the drilling fluid 130 returned, the flow rate vi of the drilling fluid 130 returned in the direction that in parallel with the ultrasonic beam path is directly projected on to the axial direction (i.e. z axle direction), to calculate the axial flow rate vz of the drilling fluid 130 returned, i.e. the flow rate component vz in z axle direction. However, in actual operation, the drill bit would move frequently, further, when the drill bit moves, it would be obvious that the contribution of the horizontal flow rate component vR of the drilling fluid 130 returned, at this time, it cannot be ignored that the horizontal flow rate component vR of the drilling fluid 130 returned. Under this condition, that the axial flow rate vz and the horizontal flow rate component vR of the drilling fluid 130 returned by utilizing one ultrasonic sensor could not be calculated, i.e. the two-dimensional flow rate of the drilling fluid 130 returned. Further, the horizontal flow rate component vR could be divided as the flow rate component vx in the x-axle direction and vy in y-axle direction. Therefore, the flow rate components vx, vy and vz of the drilling fluid 130 returned in the x-axle, y-axle and z-axle direction could not be calculated by utilizing one ultrasonic sensor, i.e. the three-dimensional flow rate of the drilling fluid 130 returned.
Therefore, it is necessary to provide an improved system and method to solve at least one of the above-mentioned problems.